Arch bridges with truss girder decks are common. The arch can be either above or below the deck with vertical members interconnecting the deck and the arch. Being in compression the arch transmits the dead and live loads on the bridge to the abutments to which the arch ends are attached. Common practice is to use the truss girder to stiffen the deck while the arch is employed as the primary load carrying member. When the arch is positioned above the bridge deck a plurality of spaced apart vertical hangers interconnect the arch and the deck, the hangers being in tension to carry the live loads on the bridge and keep the truss girder from deflecting under its own dead load.
Methods have been devised to use tension members under the bridge deck to provide an equalizing upward force on the arch hangers in order to reduce the otherwise significant structural size of the arch. However, the corresponding increase in other structural members to properly anchor or support the tension members usually offsets any cost reduction in the arch supports. Such a structure is disclosed in U.S. Pat. No. 6,892,410 for Reinforcement Structure of Truss Bridge or Arch Bridge.
Accordingly, it is the primary object of the present invention to provide a method and bridge apparatus for simplifying arch bridge construction and reducing its cost.
Another object of the invention is to provide apparatus in an arch bridge having a truss girder supported deck to balance the loads and create stability in the bridge.
A more specific object of the invention is to provide an arch bridge structure where a simple tension member will allow the truss girder that carries the bridge deck to assume the dead load of the bridge while a lighter and less costly arch structure carries the live load.
A further object of the invention is to provide an arch bridge where the tension forces in the hangers depending from the arch structure and the tension forces in supplementary tension members that span the lower portion of the truss girder can be independently adjusted to selectively vary the sharing of the live and dead loads between the arch and the truss girder.
Other and still further objects, features and advantages of the invention will become apparent upon a reading of the following description of a preferred form of the invention, taken in conjunction with the accompanying drawings.